6wd bouncing when turning

[Bstep]

Stiffness will be a factor, but as you mentioned in the original post, the back two wheels are the ones in contact with the floor due to CG placement. This will inherently cause scrubbing because a four wheeled drive base cannot turn without a component of movement perpendicular to that of the wheels rotation. The point of the 2 lowered center wheels is to keep weight off of the four wheels on the outside corners of the drive base (the ones that scrub) but since the rear four wheels are in contact, you essentially created a four wheeled drive base within your six wheeled base. This means the scrubbing is unavoidable, you will only be able to reduce the severity of the bumpy turns by making your frame stiffer.